Heat exchanger and method

ABSTRACT

A novel heat exchanger and method of heat exchange with a tank for housing a heat transfer fluid, a heater for heating the heat transfer fluid, and a coil around the heater for receiving and delivering a process fluid to be heated are provided.

TECHNICAL FIELD

Heat exchangers.

BACKGROUND

Fluid heating systems which have a tank, a heater, a liquid medium, and a pipeline for transferring a process fluid to be heated are typically referred to as indirect heaters or indirect line heaters, since the heater does not directly heat the process fluid.

In some line heaters using firetubes as the heat source, a pressurized coil transporting the fluid to be heated is serpentine in long lengths running from the front to back within a tank and above the firetube. The firetube is positioned below the coil in the lower arc of the tank, and the coil is in the higher arc of the tank. The area of displacement may be filled with a 50/50 glycol water solution as a heat transfer medium to absorb energy from the firetube which then transfers heat to the pressurized coil. In practice, heat from the firetube is transferred to the glycol medium, after which the energy is then transferred to the pressure coil to preheat, for example, a process fluid such as natural gas under pressure.

SUMMARY

There is disclosed a heat exchanger having a tank filled or to be filled with a heat transfer fluid. At least partly within the tank is a heater for heating the heat transfer fluid. The heater is arranged within the tank to be in contact with the heat transfer fluid when heat transfer fluid is in the tank. There is also a coil for transporting a process fluid to be heated wound around the heater with a gap between the coil and the heater. The coil extends between an inlet and outlet, for respectively receiving a process fluid to be heated and delivering the heated process fluid. The heater and the coil may be mounted to opposed ends of the tank. The heater and coil may also be mounted to plates that seal opposed ends of the tank.

There is also provided a method of heat exchange, the method including the steps of filling a sealed tank with a heat transfer fluid, heating the heat transfer fluid with a heater, winding the coil around the heater and leaving a gap between the coil and heater, receiving a process fluid to be heated through an inlet extending from the coil, and delivering the heated process fluid through an outlet extending from the coil.

In various embodiments, there may be included any one or more of the following features: the tank is cylindrical and has a first end at least partly supporting the heater and a second end, opposed to the first end, at least partly supporting the coil; the coil extends through the second end at two locations; the tank contains heat transfer fluid; the heat transfer fluid comprises glycol; an expansion chamber connected to or forming part of the tank for receiving expanded heat transfer fluid; the heater comprises a firetube burner; the firetube burner comprises a multi-pass firetube; a sensor on the coil; the sensor comprises a temperature sensor at one of the inlet of the coil and outlet of the coil; a structure supporting at least one of the enclosure, heater, and coil; the gap between the heater and the coil is sufficiently large to avoid corrosive electric currents passing between the coil and heater; the step of directing overflowing heat transfer fluid into an expansion chamber; the step of measuring characteristics of the process fluid as it flows through the coil.

The foregoing summary is not intended to summarize each potential embodiment or every aspect of the subject matter of the present disclosure.

These and other aspects of the device and method are set out in the claims.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:

FIG. 1 is an exploded perspective view of a heat exchanger with a U-shaped firetube, according to one embodiment.

FIG. 2 is a top plan cross-sectional view of the heat exchanger of FIG. 1.

FIG. 3 is a side elevation cross-sectional view of the heat exchanger of FIGS. 1 and 2.

FIG. 4 is a side view of a coil mounted to one plate, according to the heat exchanger of FIG. 1.

FIG. 5 is a perspective view of the plate and coil of FIG. 4

FIG. 6 is a front elevation view of the plate and coil of FIGS. 4 and 5.

FIG. 7 is a top plan view of a U-shaped firetube found in the embodiment as shown in FIGS. 1-3.

FIG. 8 is a side elevation view of a 4-pass firetube and plate according to another embodiment.

FIG. 9 is a front elevation view of the firetube and plate of FIG. 8.

DETAILED DESCRIPTION

Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

In one particular embodiment as illustrated in FIG. 1, heat exchanger 100 comprises a tank 102 containing a heat transfer fluid. Tank 102 may be cylindrically shaped or any other appropriate shape and material for containing a fluid.

There is a heater at the one end of the tank for heating the heat transfer fluid. In this particular embodiment, the heater is a firetube burner. Firetube 104 is attached to a cap 114 at one end of the tank 102, which is sealed using fastening means. A flame produced by burner 124 enters the firetube 104 through firetube inlet 106, and exhaust exits the firetube through the firetube chimney 108. In addition to the U-shaped firetube 104 as shown in FIGS. 1-3 and 7, the firetube burner may also be comprised of a multi-pass coil to further increase heating energy while maintaining a small footprint for the system, as shown in FIGS. 8 and 9, which comprise a 4-pass firetube 204. It should be appreciated that while the exemplary embodiments provide a firetube type burner, other types of heaters may also be used as the heating source.

For natural gas heating systems, the heat transfer fluid may be a solution of water and/or glycol. Glycol may be used where higher heat transfer fluid temperatures are required, and glycol may be mixed with water as a heat transfer fluid where lower freezing temperatures are required, such as in cooler climates. In addition, an expansion chamber 120, as shown in FIG. 1, may be connected to or form part of the tank 102 to address the issue of expansion of the heat transfer fluid as temperature increases. Expansion chamber 120 creates additional space for expanded heat transfer fluid such as glycol so it does not exceed the maximum volume allowed by the tank 102.

Also provided within the heat exchanger is a coil 110 for transporting a process fluid to be heated. The process fluid may be a gas such as natural gas, or any other fluid including but not limited to an explosive fluid, light oil, or liquefied natural gas. The system can also be used for heating and vaporizing liquefied natural gas.

As shown in FIGS. 1-3, the coil 110 is arranged such that it is wound around the firetube 104 but does not make contact with the firetube, leaving a gap between the coil 110 and the firetube 104. The gap should be minimized to enhance heat transfer but should be sufficiently large to avoid corrosive electric currents passing between heater and coil. FIGS. 2-3 are cross-sectional views of the heat exchanger according to one embodiment. As shown in these figures, the coil 110 winds around the firetube 104 while leaving a gap between the coil 110's inner radius and the surface of the firetube 104.

A smaller gap may result in greater heating efficiency. The coil 110 carrying the process fluid may be heated by the hottest part of the heat transfer fluid, i.e., the fluid closest to the firetube 104. Heating efficiency is further increased since heat radiating from the firetube 104 is trapped by the coil 110 which forms a wall around the firetube 104. However, the gap between the inner radius of the coil 110 and the firetube 104 should not be so small that arcing occurs between heater and coil.

By having a coil wrapped around a heater, a small footprint of the heat exchanger may be obtained.

According to the specific embodiment found in FIG. 1 and as shown in greater detail in FIGS. 4-6, the coil 110 is supported by a plate 112 that seals one end of the tank. In this particular embodiment, the coil extends through one end at two locations, inlet 116 and outlet 118. This particular configuration makes the coil 110, together with both inlet 116 and outlet 118, detachable from the rest of the tank 102. Both ends of the tank 102 may be sealed using bolts and nuts as shown in the figures, although other fastening means may be used. Furthermore, a sensor, such as a temperature sensing means may be added to both the inlet 116 and outlet 118 of the coil 110, to allow for accurate measurement of the process fluid temperature at both steps in the process.

This particular design allows for simpler manufacture and assembly, and also allows the heat exchanger to be more easily maintained, due to the fact that the tank, the heater and coil can all be separately manufactured, cleaned and repaired. However, it should be appreciated that alternative designs could be made without departing from the scope of the claims, for example, where the heater and coil do not necessarily form part of the plate, or any other arrangement where the coil 110 wraps around the firetube 104.

Although not required, the embodiment as shown in FIGS. 1-3 is supported by a support structure 122, which is used for supporting and transporting the heat exchanger 100.

Exemplary methods provide a method of heat exchange, the method comprising the steps of filling a tank with a heat transfer fluid, heating the heat transfer fluid with a heater at least partly within the tank, winding a coil around the firetube with a gap between the coil and firetube, receiving a process fluid to be heated through an inlet extending from the coil, and delivering the heated process fluid through an outlet extending from the coil.

It will be apparent that various other changes and modifications can be made without departing from the scope of in the claims. For example, the particular dimensions and characteristics of each of the individual elements may be varied. According to one embodiment, there is a 30-65,000 Btu/hr firetube within a 20″×36″ tank, with a coil with CRN approval from 20′ to 220′. In this particular embodiment, the coil is wrapped 15″ ID to 17″ ID 40′ in length, with a 4″×60″ firetube delivering the volumetric requirements. There may also be a 18-30,000 Btu/hr unit with a 16″×36″ tank and a 1″ wrapped 12″ ID 13½″ OD and 20′ of coil to deliver the heat transfer needed. Based on this particular embodiment, a 3″ firetube 60″ in length supplies the volumetric requirements. The provided heat exchangers can support firetube heaters with heat transfer of up to and beyond 3 MM Btu/hr, with appropriate adjustments to the other components of the system.

Standard safety procedures should be followed. A flame arrestor, for example of the crimped ribbon type, should be provide on the end of the tank to attenuate flame fronts passing through the heater. If glycol or like fluid is used for the heat transfer medium, then the glycol needs level control and an expansion chamber. The amount of heating should be regulated so that the exit process fluid temperature exceeds 5 C or other preset amount as needed for the process fluid line. Thermocouples may be used to detect the inlet and outlet process fluid temperatures, and the glycol temperature, and the heat produced by the heater adjusted accordingly.

In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims. 

1. A heat exchanger comprising: a tank for containing a heat transfer fluid; a heater at least partly within the tank, the heater being arranged within the tank to be in contact with the heat transfer fluid when heat transfer fluid is in the tank; a coil for transporting a process fluid to be heated, the coil being wound around the heater with a gap between the coil and the heater; and the coil extending between an inlet and outlet for respectively receiving process fluid and delivering heated process fluid.
 2. The heat exchanger of claim 1, in which the tank is cylindrical and has a first end at least partly supporting the heater and a second end, opposed to the first end, at least partly supporting the coil.
 3. The heat exchanger of claim 2, in which the coil extends through the second end at two locations.
 4. The heat exchanger of claim 1, wherein the tank contains heat transfer fluid.
 5. The heat exchange of claim 4, in which the heat transfer fluid comprises glycol.
 6. The heat exchanger of claim 1, further comprising an expansion chamber connected to or forming part of the tank for receiving expanded heat transfer fluid.
 7. The heat exchanger of claim 1, wherein the heater comprises a firetube burner.
 8. The heat exchanger of claim 7, wherein the firetube burner comprises a multi-pass firetube.
 9. The heat exchanger of claim 1, further comprising a sensor on the coil.
 10. The heat exchange of claim 9, in which the sensor comprises a temperature sensor at one of the inlet of the coil and outlet of the coil.
 11. The heat exchanger of claim 1, further comprising a structure supporting at least one of the enclosure, heater, and coil.
 12. A method of heating a process fluid comprising the steps of: filling a tank with a heat transfer fluid; heating the heat transfer fluid with a heater located at least partly within the tank; winding a coil around the heater with a gap between the heater and the coil; receiving a process fluid to be heated through an inlet extending from the coil; heating the process fluid as it passes through the coil; and delivering the heated process fluid through an outlet extending from the coil.
 13. The method according to claim 12, wherein the gap between the heater and the coil is sufficiently large to avoid corrosive electric currents passing between the coil and heater.
 14. The method according to claim 12, further comprising the step of directing overflowing heat transfer fluid into an expansion chamber.
 15. The method according to claim 11, further comprising the step of measuring characteristics of the process fluid as it flows through the coil. 